Speed-changing mechanisms of a variety of types have long been well known. Those with which the present invention is concerned are of a class in which special forms of "gearing" are preferably exploited to promote transmissions of power while involving relatively small bulk, and but few parts which desirably move at relatively slow speeds. The "gearing" preferred for such purposes comprises paired internally-toothed "sun" and externally-toothed "planet" gears in which substantially continuous rolling contacts occur between many teeth which are simultaneously in torque-transmitting engagements. So-called "geroter" gears have such characteristics, and are described in U.S. Pat. No. 1,682,563 - Hill, for example, where the interior gear has one less tooth than the exterior gear surrounding it. One such pair of gears has been described in the context of speed reduction and reversal, in U.S. Pat. No. 3,304,808 - Grant. In another speed reducer, U.S. Pat. No. 2,874,594 - Sundt, two sets or pairs or undulating-toothed gears are employed, with balls or rollers interposed between them, and with the "gears" being of different diameters. The latter fact, involving gear diameters which are different for the plural sets, represents a difficulty in relation to purposes of the present invention, and is found to be a characteristic of conventional forms of spur gearing, where different speed ratios are to be realized within the framework of like torque-transmitting capabilities. Spur gearing arrangements otherwise having some features of background pertinence to the disclosures here are believed to appear in U.S. Pat. No. 2,108,384 - Moisy, and U.S. Pat. No. 3,056,315 - Mros, and U.S. Pat. No. 3,429,393 - Lorence, and U.S. Pat. No. 2,667,089 - Gregory, and U.S. Pat. No. 3,144,791, and U.S. Pat. No. 3,783,712 - Colinet, and U.S. Pat. No. 1,770,035 - Heap et al., and U.S. Pat. No. 2,250,259 - Foote, Jr., and U.S. Pat. No. Re.24,288 - Nanni, and U.S. Pat. No. 3,192,799 - Pamplin, and U.S. Pat. 3,383,931 - Patterson, Jr. Further, my own U.S. Pat. No. 3,574,489 discloses certain orbital drives in which the gearing is of configurations akin to those preferred for the present purposes.
A form of hitherto-known gearing which lends itself especially well to uses in the mechanical drives of this invention includes an internal planet gear having "cycloidal" shape teeth or lobes of epitrochoid curvature cooperating with a surrounding external sun gear wherein the teeth are in the form of cylindrical pins or rollers and exceed by one the number of teeth of the planet gear. My U.S. Pat. No. 3,998,112, discloses improved and advantageous drives in which such gearing sets are interchangeable to make possible the production of a line of like devices which feature many and widely-different speed ratios. Such results are there promoted through application of at least two sun-and-planet gear sets wherein the interchangeable planet gears have the same diameter and the same mass eccentricities, and thus remain matched with counterweighting despite their different numbers of teeth, and wherein the cooperating sun gears are likewise all of the same diameter and have their teeth conveniently disposed at one predetermined radial distance from a central axis. There are certain speed ranges which may instead be served by single-stage speed changer, involving but a single sun-and-planet gear set; however, one then encounters the problem of developing controlled interactions between an orbiting "gear" and a relatively-fixed structure. For such reasons, the aforementioned U.S. Pats. Nos. 3,304,808 and 1,770,035 and 3,383,931 show the uses of circular arrays of critically-dimensioned and critically-disposed circular holes in orbiting gears, those holes being in surrounding mated relationship with smaller-diameter cylindrical pins and cooperating with them to effect desired motion translations. The present invention intentionally avoids the use of through-hole arrays, and, instead, uniquely employs a circular transmission-plate or cam which has open circular-sided depressions about its periphery cooperating with smaller cylindrical pins or rollers; such a transmission-plate or cam may advantageously be substituted for a lobed cam as employed in the devices disclosed in my aforesaid Patent.